Beefsteak: first comment: just because you are ingesting the same amount of things each day, does not mean your body is absorbing identical amounts after each intake. Stomach emptying time, amount of fat in the mean/snack, other foods, etc., all can contribute to the amount (rather the concentration) of the key item as it travels along the tract. If different amounts are absorbed, the effects on your arteries may be variable.

Other items I just found after some searching are anything containing nitrites (hot dogs, bologna, pepperoni), garlic (which you say you are already taking) [actually, the list of beneficial characteristics of garlic for helping heart disease is really neat and I may add this to my list], cocholate (really a vasocontrictor from the caeffine)...many of the site hits relate to migraines.